1. Field of the Invention
The invention relates generally to subsurface motors of the type that are used within electrical submersible pumps (ESP's). In particular aspects, the invention relates to techniques for monitoring operational parameters of such motors using fiber optics.
2. Description of the Related Art
Electrical submersible pumps (ESPs) are routinely used in the production of hydrocarbon from wells. A typical ESP includes a downhole motor that converts the mechanical power to operate a pump and associated components, such as a gas separator. Downhole motors include a stator and a rotor that is rotationally moveable with respect to the stator. A housing surrounds the stator and rotor.
Conventionally, optic fibers have been placed within an ESP motor by disposing them either entirely outside of the motor (i.e., mounted outside of the motor housing) or within a sealed area of the motor such as the winding compartment, which is filled with epoxy or varnish sealant. The use of fiber optic sensors within the sealed winding chambers of the stator of the motor is discussed in U.S. Patent Publication no. 2011/0002795 by Brookbank. Because U.S. Patent Publication no. 2011/0002795 is owned by the assignee of the present application, U.S. Patent Publication no. 2011/0002795 is herein incorporated by reference in its entirety. In Brookbank, the optic fibers are located within the winding chambers alongside electrical conductors that pass through the winding chambers. The fiber is disposed through the winding chambers by looping it through substantially opposing sides of the stator. This permits the fiber to provide two parallel legs. Bending or deformation of the stator will place one of the opposing legs in tension and the other in compression. Optical discontinuities on each of the legs will be moved axially, and the detection of this relative axial movement allows measurement of bending or deformation of the stator. Placement of the fibers in this manner makes the fibers largely incapable of detecting certain operating parameters, such as temperature, since the fibers and their surrounding protective tubes are sealed within material that is largely insulative and precludes transfer of heat.